1. Field of the Invention
This invention relates to an ink-jet recording device that records on a recording medium by ejecting ink from nozzles, and more specifically it relates to the structure of a pump disposed in part of an ink supply path that supplies ink to the nozzles or in an ink discharge path that discharges ink from the nozzles.
2. Description of the Related Art
In ink-jet recording devices of the prior art, recovery devices are often proposed for returning the ink-jet head to a normal condition when the ink has become thick near the nozzles or if there are bubbles in the nozzles. Certain of these recovery devices employ a means for covering the nozzles with a cap, driving a pump disposed in the ink discharge path connected to the cap for withdrawing or discharging ink from the nozzles using pressure (negative pressure) generated by the pump.
To supply ink to the nozzles from the ink tank, there is also a supply device with a pump disposed in the ink supply path that links the tank and nozzles and supplies ink using the pressure generated by the pump.
In the pumps used in this kind of recovery device and supply device, there is a tube pump proposed that comprises a flexible tube disposed in an arc along a guide and a rotor supporting a roller which pressurizes the flexible tube and that generates pressure using deformation of the tube. In this kind of tube pump, rotation of the rotor causes the roller to sequentially squeeze the flexible tube, whereby pressure is generated inside the tube.
Japanese Laid-Open Patent Application 6-286158 discloses a tube pump wherein the rollers pressurize the tube when the rotor is rotated in the forward direction and relieves the pressure of the roller on the tube when turned in the reverse direction. The shaft of the roller of this tube pump is fitted in a channel in the body of the rotor, and depending on the direction of rotation of the rotor, the roller shaft moves to one or the other end of the channel. Due to the difference in the distance from each end of the channel to the center of the rotor, the roller moves forward or back each time the direction of rotation is changed.
A tube pump is disclosed in Japanese Laid-Open Patent Application 4-261864 wherein the roller is pushed against the tube by a spring, whereby the tube is deformed and pressurized by the pressure exerted by this spring.
The tube pumps described above, however, present the following problems.
In the pump disclosed in Japanese Laid-Open Application 6-286158, the amount with which the roller squeezes (intrudes on) the tube is affected by the distance from the center of the rotor to the shaft of the roller at one end of the channel, the roller diameter, the shape of the arc-shaped guide for mounting the tube, the tube wall thickness and the accuracy with which these parts are attached. Therefore, even if parts are used that are not completely desirable from a tolerance standpoint with respect to the dimensional accuracy and assembly accuracy of these parts, there must be no space in the tube (tube must be completely squeezed) where the roller pressurizes it in order for the pump to be effective.
Therefore, a large motor with a large output is used to drive the rotor so that the motor will have enough torque even if the roller should intrude too far, which can result from fluctuations in the amount the roller intrudes due to limits in the accuracy of the parts and their assembly accuracy. This is disadvantageous from the perspective of increased cost as well as increased size of the motor.
In the tube pump disclosed in Japanese Laid-Open Patent Application 4-261864, a configuration is employed that uses a spring to urge the roller which squeezes the tube, and therefore it is possible to avoid having to increase the torque to drive the pump.
However, since the roller is continually urged by the spring and presses against the tube in this kind of tube pump, it causes certain problems. That is, in this kind of pump, when the roller is positioned so that it pressurizes the tube on the arc-shaped guide, pressure is continually applied to the tube and the tube becomes deformed. If the roller is left in this condition for long periods, then plastic deformation occurs in the tube and the tube deteriorates and becomes damaged. Therefore, when the pump is not operating, the roller must be continually parked in a position away from the tube on the guide. This requires a photo sensor or other type of detector to determine the position of the roller (i.e., pump phase). The addition of the photo sensor or other detection means increases cost and makes the pump larger.